Research Interest:

The research in our group follows two major directions. In one, we are studying the role of small non-coding RNAs as mobile instructive signals in development. In the other, we are dissecting mechanisms underlying shoot stem cell homeostasis and organogenesis. In our research we use maize, Arabidopsis thaliana, and the moss Physcomitrellapatens as model organisms, as each offers unique experimental advantages and because comparative studies can provide an evolutionary perspective on key genetic pathways.

1) Small RNAs as mobile positional signals in development

Multicellular organisms depend on cell-to-cell communication to coordinate development. Recent findings revealed that in addition to peptide ligands, transcription factors, and hormones, plants use small RNAs as positional instructive signals. An obvious advantage of employing mobile small RNAs is that they represent a distinct class of signaling molecules that possess high specificity and whose movement can, in principle, be regulated independently from that of other developmental signals. Moreover, mathematical modeling predicts that mobile small RNAs have the intrinsic property to generate sharply defined on-off boundaries of target gene expression, a prediction for which our preliminary data provide compelling experimental support.

Major questions regarding the properties and function of mobile small RNAs in development, however, remain: how do small RNAs move, how is their mobility regulated, what are the distinguishing patterning properties of mobile small RNAs, and how might opposing signal gradients interact to achieve the remarkable precision and robustness of developmental programs? We combine classical genetics with quantitative imaging and theoretical approaches to address these questions in model plants, such as Arabidopsis, maize, and moss. This information will be used to understand the interplay of signals that coordinate the many patterning processes occurring in close spatial and temporal vicinity within the developing organism.

Figure 1. Gradients of mobile small RNAs have morphogen-like patterning activities. Mobility of miRNAs from their site of biogenesis in the bottom epidermis (A) yields a miRNA gradient (B) that through a threshold-based read-out establishes an on-off pattern of target gene expression (C,D).

Figure 2. Synthetic system to study miRNA mobility. In seedlings expressing fluorescent reporters (A), artificial miRNAs targeting these reporters are expressed in a regulated often tissue-specific manner (B) to arrive at the parameters and mechanisms of miRNA mobility (C).